The invention relates generally to ultrasound imaging systems, and more particularly, to contrast imaging systems.
Contrast imaging scanning is an ultrasound technique used for various clinical studies. For example, it may be used to study the flow of blood through a body of a patient who is to be scanned. Contrast imaging includes injecting contrast agents in the body of the patient. The injected contrast agents provide a better visualization of blood flow, for example, in the study of flow of blood.
Contrast agents for ultrasound imaging typically include encapsulated gas bubbles that have a diameter less than ten microns. These bubbles enhance the amplitude of back-scattered ultrasound signals. The back-scattered ultrasound signals are the ultrasound signals that return back after getting reflected from the parts of the body being scanned. The enhanced amplitude results from bubble reflection and/or bubble destruction. The amplitude of the ultrasound signal is enhanced as the ultrasound signal is reflected from an interface between two objects or materials, for example, from the interface of tissues and contrast agents. Bubble destruction inside the body of the patient also enhances the amplitude of the back-scattered ultrasound signals. The amount of reflection and bubble destruction depends on the power of the ultrasound signals. The power of the ultrasound signals is often referred to as an acoustic power output of the ultrasound signals. Acoustic power output is usually measured as the amount of ultrasound energy delivered per unit time. The acoustic power output further may be represented or defined by a Mechanic Index (MI) value.
A low MI value (e.g., MI<0.2) enhances amplitude through reflection. A high MI value (e.g., MI>0.2), however, enhances amplitude through bubble destruction. Bubble destruction can result in an intermittent scan. Intermittence is introduced as new bubbles need to be injected when bubbles are destroyed. Therefore, for uninterrupted scanning, low MI value contrast imaging with minimum bubble destruction is typically used.
Generally, in a contrast imaging scan, the MI value of the ultrasound signals is set before injecting the contrast agents in the body. However, the ultrasound signals can get attenuated as they travel through the body of the patient. Hence, the resultant MI value of the ultrasound signal inside the body may be less than the preset value. Further, the amount of attenuation in the MI value depends on the characteristics of the body. For example, the MI value depends on the amount of fat in the body as the attenuation of the ultrasound signals is greater in a fat layer compared to muscles. Therefore, when the amount of fat in the body is high, the MI value of the ultrasound signal inside the body is less.
In order to maintain the required MI value in the body, doctors adjust the setting of the MI value during a contrast imaging scan. However, this adjustment is performed manually and may lead to important information getting lost while the setting is adjusted. For example, for the scanning of a liver tumor, the first few seconds in an artery phase ultrasound scan are very important.